dm: remove fmode_t argument from .prepare_ioctl hook

Use the fmode_t that is passed to dm_blk_ioctl() rather than
inconsistently (varies across targets) drop it on the floor by
overriding it with the fmode_t stored in 'struct dm_dev'.

All the persistent reservation functions weren't using the fmode_t they
got back from .prepare_ioctl so remove them.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index ff751b0..9929721 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -130,8 +130,7 @@ static void linear_status(struct dm_target *ti, status_type_t type,
 	}
 }
 
-static int linear_prepare_ioctl(struct dm_target *ti,
-		struct block_device **bdev, fmode_t *mode)
+static int linear_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
 {
 	struct linear_c *lc = (struct linear_c *) ti->private;
 	struct dm_dev *dev = lc->dev;